The ecoregion extends southwest from the Amazon River between its large Madeira and Tapajós tributaries, and crosses the border into Bolivia.

[2] To the northwest the ecoregion is separated from the Purus-Madeira moist forests by the Madeira River, which has Monte Alegre várzea along much of its length.

[2] At its northern boundary on the Amazon river the elevation is 20 metres (66 ft) above sea level.

[1][a] The terrain here consists of table mountains with rocky meadows and semi-deciduous open submontane forest and woodland savanna.

The clearwater Tapajós, which rises in the ancient and well-weathered Brazilian Shield and follows a fixed course, does not carry sediment.

[citation needed] The ecoregion is in the Neotropical realm and the tropical and subtropical moist broadleaf forests biome.

There is white sand flooded igapó forest along the clearwater Tapajós and Aripuanã rivers, with large trees such as Triplaris surinamensis, Piranhea trifoliata, Copaifera martii and Alchornea castaneifolia.

[2] On the upper Madeira and Tapajós there are large areas of campina, white sand grasslands.

The montane forests of the upper Marmelos and middle Tapajós hold Hevea camporum, Euterpe longibracteata, Huberodendron ingens and Brachynema ramiflorum.

The bare-eared squirrel monkey (Saimiri ustus) and red-bellied titi (Callicebus moloch) are found only in the south-central Amazon.

Other mammals include white-lipped peccary (Tayassu pecari), collared peccary (Pecari tajacu), cougar (Puma concolor), jaguar (Panthera onca), South American tapir (Tapirus terrestris) and brocket deer (Mazama genus).

[2] Endangered mammals include the white-cheeked spider monkey (Ateles marginatus), white-nosed saki (Chiropotes albinasus) and giant otter (Pteronura brasiliensis).

The banks of the Tapajós and Madeira have large areas that are scarred by large-scale illegal mining.